Polyethers with molecular weights above 3500 having terminal primary amino functionality are an important class of polymers having a variety of uses. These polyethers may be reacted with epoxy resins to create tough infusible plastics as well as elastomeric vulcanizates. Further, these polyethers may be reacted with diisocyanates to create polyurea block copolymers. It is very important for such applications that the amine terminated polyether precursors be as purely difunctional as possible, i.e., have no terminal hydroxyl, halide, or other inert functionality, in order to maximize the degree of polymerization of the desired products as well as their performance.
U.S. Pat. No. 3,436,359 discloses polyether diamines with a high degree of terminal primary amino groups. These polyethers were obtained by capping the highly difunctional bis-oxonium ions resulting from the reaction of cyclic ether monomers and trifluoromethanesulfonic anhydride with anhydrous ammonia. However, it is difficult to carry out this process without obtaining polyether diamines contaminated with certain amounts of secondary amine groups (up to 3%) as well as smaller amounts of tertiary amino nitrogens (up to 0.3%) in the chain which provide a primary amine terminated polyether branch or side chain. It is especially difficult to control the level of formation of these by-products when the process is carried out on a large scale. Although such mixtures are useful in a number of applications, polyether diamines containing even these low levels of multifunctional impurities are unsuitable for the preparation of high molecular weight soluble polyether-polyurea block copolymers from the reaction of polyether diamines with stoichiometric molar ratios of diisocyanates. These in-chain secondary amines and primary amine terminated tertiary side chains provide additional sites on the polymer chain which result in crosslinking upon reaction with diisocyanates. This typically results in unprocessable gels.